1. Field of the Invention
The disclosure relates to LED driving techniques, and more particularly, to an LED driving device, LED device and driving method thereof capable of avoiding being damaged by high voltage.
2. Description of the Prior Art
Due to environmental concerns and technology advancements in recent years, light-emitting diodes (LEDs) have gradually replaced cold cathode fluorescent lamps (CCFLs) as screen backlights of computers and TVs.
Please refer to FIG. 1, which is a schematic diagram of a conventional LED device 10. The LED device 10 includes an LED string C1 and an LED driving chip 102. The LED driving chip 102 includes an LED driving circuit 104, a short detection circuit 106 and a boost circuit 108, for driving, performing short detection on, and providing a boost voltage Vbst for the LED string C1, respectively. Noticeably, FIG. 1 only illustrates one LED string, one short detection circuit and one driving circuit for simplicity. However, the LED device 10 can practically include a plurality of LED strings connected in parallel, a plurality of short detection circuits, and a plurality of driving circuits. Each of the plurality of LED strings is similar to the LED string C1, and is driven, monitored for shorts and provided with a boost voltage by the corresponding driving circuit, short detection circuit and boost circuit of the LED driving chip 102.
In detail, during normal operation, the LED driving circuit 104 generates a control signal Sctrl according to a feedback voltage Vfb from LED string C1, i.e. a bottom voltage Vbtm of LED string C1, and provides the control signal Sctrl to the boost circuit 108. Then, the boost circuit 108 adjusts the boost voltage Vbst according to the control signal Sctrl, so as to keep the feedback voltage Vfb and the boost voltage Vbst, around 20-60V, within a reasonable range. However, under some circumstances, e.g. when the LED driving circuit 104 controls the LED string C1 to blink, or the short detection circuit 106 detects an LED short, the LED driving circuit 104 cuts off a driving current Id of the LED string C1, such that the bottom voltage Vbtm of the LED string C1 rises to the boost voltage Vbst, i.e. the feedback voltage Vfb rises to the same high voltage level as the boost voltage Vbst.
The conventional LED driving chip 102 is manufactured in a high operating voltage process, so the LED driving circuit 104 can receive the high voltage level without being damaged. However, due to a current trend toward system on chip (SOC) architectures, the LED driving chip is increasingly integrated with image processing circuits, and is also manufactured in a low operating voltage process with an operating voltage no higher than 5V to achieve higher operating speed. Thus, in consideration of high possibility that a low operating voltage chip is burned out when receiving a high voltage, there is a need for improvement of the prior art to adapt to the trend toward low-voltage single chips.